1. Field of the Invention
The invention relates to an X-ray examination apparatus, including an imaging screen for forming an image of an object or body to be examined, an image pick-up device having a pick-up face for converting said image into electric signals, and at least one illumination element for illuminating the pick-up face.
2. Description of the Related Art
An X-ray examination apparatus of this kind is known from U.S. Pat. No. 4,359,759. The cited document describes an X-ray apparatus which comprises an X-ray source for generating X-ray radiation whereby a part of a patient to be examined is irradiated. The shadow image thus formed is received by an image intensifier which forms an optical representation of the shadow image on the imaging screen. The optical representation is transferred, via an optical system, to the pick-up face of a television camera, after which the image can be processed by a signal processor and/or displayed on a monitor. The response time of the pick-up face of the television camera improves when light is incident thereon. Consequently, the optimum response time of the television camera is obtained only some time after activation of the X-ray source. This leads to a radiation load for the patient without diagnostically useful images being acquired. In order to achieve that the television camera has the desired response time already when the X-ray source is switched on, the known apparatus comprises a number of light-emitting diodes (LEDs) which are arranged on or in a plexiglass ring around the optical path from the image intensifier to the television camera. The side of the plexiglass ring facing the television camera is roughened so as to achieve diffusion of the light and hence uniform illumination of the pick-up face of the television camera.
It has been found that such a ring of LEDs is not very well suitable for obtaining a uniform light distribution on the pick-up face of the television camera. A second drawback of the known apparatus consists in that the plexiglass ring must be arranged at a sufficient distance from the television camera in order to ensure that the light emitted by the LEDs is incident on the pick-up face. This imposes restrictions in respect of the optical system between the image intensifier and the image pick-up device. Notably the realisation of a very compact construction of this part of the X-ray apparatus is hampered thereby. A further drawback consists in that the inner edge of the ring may be a source of undesirable reflections which may give rise to artefacts in the image picked up by the television camera.